If you keep your eyes peeled when King Joffrey takes Sansa Stark to gaze
upon the spiked head of her dead father around 12 minutes in, you'll notice
that one of the heads looks slightly familiar. Show creators David Benioff
and D.B. Weiss explained in their DVD commentary (from Season 1, episode
10) that the decapitated head is actually George Bush. This was discovered
by redditor SidIncognito.

Game of Thrones producers David Benioff and D.B. Weiss acknowledged it:

What happened was this: we use a lot of prosthetic body parts on
the show: heads, arms, etc. We can't afford to have these all made from
scratch, especially in scenes where we need a lot of them, so we rent
them in bulk. After the scene was already shot, someone pointed out
that one of the heads looked like George W. Bush.

In the DVD commentary, we mentioned this, though we should not
have. We meant no disrespect to the former President and apologize if
anything we said or did suggested otherwise.